Natural lipids and oils are used in pharmaceutical preparations, food products, cosmetics, and various industrial products such as lubricants, coatings, inks, paints, plastics and the like. Such lipids are subject to oxidative degradation which can affect color, odor, viscosity, and lubricity characteristics thereof, adversely affecting the quality of the commercial products containing such lipids. In the food, cosmetics and pharmaceutical industries, maintaining high quality color and odor of oils and other lipids is important to avoiding oxidation-induced rancidity which is affected by factors such as the oxygen concentration, light and heat, as well as the degree of unsaturation of the lipid or oil, and the amount of natural or synthetic antioxidants present therein. Biodegradable lipids, oils and derivatives thereof used as cutting lubricants are recognized to be adversely affected by heat induced oxidation.
Meadowfoam (Limnanthes alba) seed oil has been demonstrated to be highly stable to oxidation. Although the identity of the compound(s) responsible for exceptional oxidative stability of meadowfoam oil is heretofore unknown, mixing meadowfoam oil with other oils imparts enhanced oxidative stability to the mixture. (Isbell, T. A., Abbott, T. A. and Carlson, K. D. 1999. Ind. Crops Prod. 9(2):115–123). Several minor constituents in meadowfoam oil which either diminish oxidative stability or impart small increases in oxidative stability of meadowfoam oil are known, however. (Abbott, T. P. and Isbell, T. A. 1998. Abstracts of the 89th American Oil Chemist's Society Annual Meeting & Expo, Chicago, Ill., May 10–13, 1998. p 66). Refined meadowfoam oil (and other refined seed oils and vegetable oils) exhibit reduced oxidative stability as a result of the refining process. Meadowfoam is known to contain 3-methoxyphenyl actetonitrile, 3-methoxybenzyl isothiocyanate and 3-methoxybenzaldehyde. When added to refined meadowfoam oil at levels from about 0.1% to 1.0%, these compounds exhibit only small to moderate antioxidative effects, at best.
Thiourea has been shown to possess antioxidative activity in oils (Kajimoto and Murakami Nippon Eiyo, Shokuryo Gakkaishi 51(4):207–212, 1998; Chemical Abstract 129:188538); but thiourea is not very soluble in oils. The oxidative stability of ester-based synthetic lubricants (i.e., not vegetable oils) stabilized with amine antioxidants has been shown to be enhanced with specific thioureas (Chao and Kjonaas Amer. Chem. Soc. Preprints, Div. Pet. Chem. 27(2):362–379, 1982). Camenzind and Rolf, Eur. Pat. Appl. EP 91-810474, Chemical Abstract 117:30273, show that certain acylated thioureas are able to increase the oxidative stability to lubricants and hydraulic fluids.
Mono- and di-substituted thiourea compounds also have been described in U.S. Pat. Nos. 2,154,341, 2,662,096, 3,852,348, and 3,991,008. Migirab et al. Phytochem. 16(11):1719–1721, (1977) disclose methoxy-substituted aromatic thioureas such as N,N′-bis[(4-methoxyphenyl)methyl]-thiourea (CAS#22313-70-8), which is isolated from P. brazzeana. 
There is a need for antioxidant compounds and compositions, especially natural antioxidants or derivatives thereof, that are soluble in lipids and oils and are capable of imparting oxidative stability thereto when added at low concentrations.